Polyester cords such as polyethylene terephthalate cords are used in automobile tires for the refinforcement of carcass plies. While the cord has outstanding properties as to strength and low flat-spotting tendencies, it is relatively easily degraded by chemical means. Acids and bases are known catalysts for polyester hydrolytic degradation. During normal operation of a tire having polyester cords, it was found that the cords lost strength. The elimination of amine liberating chemicals from the rubber curing system was beneficial and lowered the rate of hydrolytic degradation.
However, in tubeless tires there is an inner liner adjacent to the carcass plies of the tire, and it is made of a composition including bromobutyl rubber and/or chlorobutyl rubber because of the ability of this rubber to retain gases (low rate of diffusion) and good adhesion to other rubbers. However, for most purposes in order to obtain superior adhesion to the carcass plies which are of high unsaturated rubbers and to obtain other rubbery properties, these halogenated butyl rubbers are blended with a substantial proportion of highly unsaturated rubber(s) such as natural rubber, SBR, etc. In curing a tire the different rubber compounds in the tread, plies or carcass layers, belts, sidewalls, interliners, beads and so forth are formulated so as to cure together properly to form a unitary or composite structure. In many cases the halobutyl rubber innerliner composition requires an amine accelerator such as a polyimino compound like di-o-tolyl guanidine which is a relatively strong base to properly cure the halobutyl inner liner compounds or compositions to the tire assembly. Only a thin layer of the polyester skim or ply stock separates the polyester tire cords from the halobutyl rubber inner liner. Br or Cl butyl rubbers are known to degrade at elevated temperatures to give Br and/or Cl or acid fragments. Also, the polyimino accelerator may give off amine fragments. These acid and amine compounds and/or their fragments can diffuse through the innerliner and through the ply or skim rubber stock to attack the polyester cord.
Accordingly, it is one object of this invention to provide a Br and/or Cl butyl rubber composition suitable for preparing an inner liner for a tire and which exhibits reduced attack on polyester cords or polyester reinforcing elements.
Another object of this invention is to provide a flexible laminate comprising a Br or Cl butyl rubber composition and a hydrocarbon rubber composition adjacent thereto and containing a plurality of polyester cords adhesively bonded thereto and which exhibit reduced loss in strength on aging, both layers preferably being sulfur cured with sulfur cure systems sufficient to cure said polymers of the compositions of said layers.
These and other objects and advantages of the present invention will become more apparent to those skilled in the art from the following detailed description and working examples.